This invention is generally in the field of devices for the administration of drugs to patients and devices for biological sample collection through the skin. More particularly this invention relates to microneedle array devices and methods for transdermal drug delivery, for transdermal diagnostic sampling of biological fluids, or for a combination thereof.
Microneedles and microneedle arrays have been disclosed for use in the fields of transdermal drug delivery and biological sample collection. Transdermal drug delivery provides several advantages over other routes for administering a drug formulation to a patient. For example, oral administration of some drugs may be ineffective because the drug is destroyed in the gastrointestinal tract or eliminated by the liver, both of which are avoided by transdermal drug delivery. Parenteral injection with a conventional hypodermic needle also has its drawbacks, as it is painful and inconvenient. It would, however, be advantageous to provide improved microneedle devices and methods for transdermal drug delivery. Analyte concentration determination in biological samples withdrawn transdermally is important for a variety of diagnostic applications. For example, collection of blood or interstitial fluids is often necessary, for example, to measure glucose for diabetes management, or to measure cholesterol for monitoring cardiovascular conditions. Conventional devices and methods may involve cumbersome and complicated devices and procedures, or may be painful. It would be advantageous to provide devices and diagnostic methods that are relatively simple to use and pain free, in order to improve patient compliance with diagnostic monitoring and disease management.
In both transdermal drug delivery and transdermal biological sampling using microneedle arrays, particularly in patch-type devices, it would be particularly desirable for the microneedles to remain in their precise, penetrated position through the stratum corneum to maintain the fluid communication between a drug or sample collection reservoir and the tissues beneath the stratum corneum for an extended period. However, the skin of a patient is contoured and quite flexible. Thus, it may be difficult for a conventional microneedle array having a rigid, planar substrate to maintain the desired microneedle penetration, particularly where the microneedle array is part of a patch device and the patient (and consequently, his or her skin) ordinarily moves about and flexes throughout the extended period of microneedle array (e.g., patch) application. For example, a microneedle array having base made of silicon is flat and inflexible, and even though a polymeric or metal microneedle base can be slightly bent in one direction, such arrays of microneedles cannot readily be applied to convex or concave skin surfaces or stretched in different directions. Thus, a patch having such a microneedle array may tend to fall off the skin surface as the patient moves, particularly for patches designed to be continuously worn even on relatively flat areas of a patient's skin, due to the significant stretching of the skin that occurs during normal movement. It therefore would be desirable to provide a microneedle array that can improve penetration control into contoured skin surfaces and lessen premature movement of microneedles out of optimum penetrated position. It also would be desirable to provide a better microneedles array, and patch, for transdermal drug delivery or transdermal biological sample collection over an extended period.